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oxy126

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  1. oxy126

    How to get to Space

    By oxy126,

    Escape velocity, at the surface of the earth, is just about a whopping 11.2 km/s. This means that, to completely escape the force of earth's gravity, from the surface of the earth with the only outside for being gravity, you would need to be going this speed to escape (ignoring, of course, drag - drag forces at those speeds would rip a spaceship apart). So on my way to physics last friday I thought about how to reach those speeds, without the use of costly rocket fuel. One (although initially very costly solution) could be to have a giant underground tunnel, throughout the entire surface of the earth, that would accelerate an object over time using electromagnetism until it reaches those speeds. As long as the tube is in a vacuum, it is more than possible to do this.

    In order to keep an object in a circular orbit, we know that the centripetal acceleration must equal mv^2/r, and this net acceleration can only come from two other sources - gravity, at a constant 9.81 m/s^2, and the force generated by our electromagnetic coils. Assuming v is terminal velocity, E is the electromagnetic force, and r is approximately the radius of the earth, we get (11.2 * 10^3 m/s)^2/(6.371 * 10^6) = 9.81 + E. Solving for this, we can determine that E = 9.88 m/s^2, only a bit more than the acceleration due to gravity. If you could somehow construct this tunnel, it would be possible to bring objects up to speeds as high as this. Most of the time, for typical space missions, it wouldn't have to be quite so large anyways.

    The real issue is getting in out of the tunnel, and through the atmosphere. Going straight into the air at such speeds would destroy a fair chunk of the surrounding area, and most certainly the payload. You would have to create a giant vacuum tunnel through the atmosphere if you wanted this to work, which not only would look strange (it would be technically 'flat' - tangential to the point of release for the most part), but be very difficult to build. But in any case, it's wishful thinking.
  2. oxy126
    Over the summer, I learned a lot about light, and I welcome the opportunity to share that with you. One thing I learned about was how different light sources stacked up against one another. Most people know that incandescent bulbs (tungsten-halogen, the "normal" kind) are less efficient that LED or fluorescent bulbs, but don't know why. I'm here to alleviate that knowledge gap.

    The reason incandescent bulbs are inefficient is because they produce a lot of heat - not just their own heat, but rather they radiate heat, in the form of infrared light waves. Eventually, all of the energy that goes into heating up the tungsten filament does get radiated out, but usually not at visible wavelengths. When an object is heated (through the addition of energy, AKA Q = mc * delta t), it begins to reemit that energy at a variety of wavelengths, until all that energy has been dispensed of. The distribution of this energy, as a function of wavelength, follows (mostly) a blackbody radiation distribution curve (see below), which shifts as a function of temperature. Most of the energy for a tungsten bulb is in the infrared region, meaning it is never actually seen. With hotter objects, however, more of the light is visible, and shifted towards lower wavelengths, which is why hot flames appear blue to our eyes.



    A tungsten bulb is usually around 3300 degrees Kelvin, so a lot of energy is lost. However, in recent years, in attempts to save energy, other light producing methods have been pursued. One of these is the use of fluorescent bulbs, which rely on molecular excitation to produce light. As discussed in chemistry, electrons falling down an energy level emit photons of a very specific wavelength.



    Above is an example spectral distribution curve. As you can see, almost all of the emitted light is in the visible region, making it much more efficient. However, because these contained dangerous chemicals oftentimes, the concept of the LED was also pursued as a potential light source. LEDs (a topic to be discussed by itself), "force" electrons to change energy levels as they flow through a circuit, through (usually) a junction between different types of doped silicon. The spectral distribution for these is, like the fluorescent, confined to a short wavelength band (usually blue). However, using a phosphor coating, which will absorb and reemit the light at different wavelengths, the light is made to look more "white" (see below).



    That, in a nutshell, displays a variety of common lightings, and why some are preferred over others. I could go into more depth, but this gives a basic overview of how we light our world.
  3. oxy126

    Makin' Noise

    By oxy126,

    Sometimes I like to sit back and pump some jams. Before the invention of all this modern technology such as speakers and cds and digital audio, such things just weren't possible. Music had to be performed. But with the invention of electrical speakers that all changing. People were able to finally jam out.
    The common speaker relies on the principles of electromagnetism. In the center is a magnet (attached to a speaker cone), surrounded by a coil. As the current through the coil fluctuates, the magnet and cone move, vibrating to reproduce the encoded sound. However, all things have inertia, so it can take time to reverse the momentum of the cone, creating a loss in audio quality in the event that the speaker cone is too heavy. Similarly, if the cone isn't stiff, it will delay its movement and creating quality losses that way as well. These losses are most noticeable with "harsher" waveforms (such as squarewave, which, as the name implies changes position very quickly at wave boundaries), or with more complex sounds, such as violin or saxophone.
    Because of these drawbacks good sound systems often have multiple speakers, all tuned to a different frequency. Subwoofers are typically larger because lower frequencies are less audible, and lower frequency waveforms are easier to reproduce in terms of speaker design. Tweeters are smaller for the opposite reasons - they need better accuracy because higher pitches involving larger shifts in momentum with respect to time, so they are typically smaller to achieve this. Also, because every material has a resonant frequency (where it will absorb a lot of energy), the materials in each are tailored to avoid this.
    Next time you're cruisin', bumpin' along to your favorite song, remember this. And invest in a better sound system.

  4. oxy126

    Gaseous Mathematician

    By oxy126,

    In the past few years, the Dyson Air Multiplier has revolutionized the field of recreational air transportation. It's for this reason that I feel it warrants a blog post, all to itself. Lauded for a lack of (visible) fan blades, it is safer than the more common axial-style fan.





    The Man Behind the Magic





    But how is this trickery pulled off? Allow me to explain.

    The Dyson Air Multiplier does, in fact, have typical fan blades. But instead of being open to the air, they are hidden in the base of the fan, and air intake is through the little gratings along the circumference of the tube. That air is then "pumped" through the upper ring and exits the fan.

    But then why is it called an "air multiplier"? Dyson claims that the fan outputs 15 times the input air volume, and it does (or at least comes close). It does this as a result of Bernoulli's Principle, which states that faster moving air has a lower pressure. Because the air in the center of the ring is slower, and therefore higher pressure, it tends to get "dragged" along behind the small amount of air that is output, bringing more air into the mix.

    Conservation of energy still applies, so yes, the air does get decelerated during this process to account for that. It still does have a fan in the base, which can be noisy in getting the air up to an acceptable speed to "multiply" it. But it is a unique and interesting concept nonetheless, and a mark in the record books for "fan"-atics like me.
  5. oxy126

    Introductions

    By oxy126,

    Hi there.

    I'm a new Physics AP-C student, and I would like to tell you a little bit about myself. I'm an avid programmer/science enthusiast, and am looking towards entering a scientific or science-related field. I (as one may assume) like science and math, and more leisurely things like playing video games or disc golfing. Things of the sort.

    The reason I'm taking Physics AP-C this year is because I'm interested in learning more about physics and I want to solve more challenging problems using my physics knowledge. I enjoy calculus and I think it will be cool to see some of the applications of what I learn. As a result, I hope to not only hone my calculus knowledge but get some useful information on specific areas of physics and, in general, how to approach difficult, complex problems in an effort to solve them.

    I always enjoyed electricity and magnetism, and I'm looking forward to that and hopefully being able to dream up some cool uses for my new knowledge. However, no matter what we learn, I think I'll be excited just to know it. So I'm hoping to have fun!

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